Production of ethylenically unsaturated aliphatic acids

ABSTRACT

The present invention relates to a process for the production of unsaturated aliphatic acids and the catalyst therefore, by the vapor phase oxidation of the corresponding unsaturated aliphatic aldehydes with molecular oxygen, optionally in the presence of steam, in the presence of an oxidation catalyst consisting of the oxides of the elements molybdenum, vanadium, rhenium, plus at least one of the oxides of magnesium, copper and cadmium.

BACKGROUND OF THE INVENTION

Catalyst compositions similar to those of the present invention areknown for the oxidation of acrolein to acrylic acid. For example, U.S.Pat. No. 3,736,354 discloses catalyst compositions containing molybdenumand vanadium that may be promoted by 17 additional elements, among whichare magnesium and copper. Phenium is not disclosed as a possiblepromoter to these catalysts.

U.S. Pat. No. 3,966,802 discloses a molybdenum-vandium catalyst that maybe promoted with alkali metal and optionally tungsten or antimony. Thehighest single pass yield of acrylic acid shown in this patent is 70.5%without the optional tungsten and 72.8% when tungsten is used as anadditional promoter.

U.S. Pat. No. 3,567,773 discloses a molybdenum, vanadium and tungstencatalyst that obtains yields as high as 89% acrylic acid.

Finally, U.S. Pat. No. 4,042,533 discloses a molybdenum, vanadium,tungsten catalyst that may be promoted by one or more of the elements ofrhenium and titania. The highest per pass conversion achieved withrhenium catalyst is noted as 87% acrylic acid.

The present invention is based upon the discovery that promoters thathave given unacceptable yields in the prior art catalyst, when combinedwith molybdenum-vanadium catalyst, achieve excellent conversions ofaldehydes to acids.

SUMMARY OF THE INVENTION

The present invention relates to an improved process for producingolefinically unsaturated carboxylic acids from the correspondingunsaturated aldehydes and to the catalyst composition utilizedtherefore. More specifically, the present invention relates to a vaporphase process for producing acrylic acid or methacrylic acid fromacrolein and methacrolein, respectively, by oxidation of the unsaturatedaldehydes with molecular oxygen, optionally in the presence of steam,and in the presence of an oxidation catalyst having the empiricalformula

    Mo.sub.a V.sub.b Re.sub.c X.sub.d O.sub.e

wherein X is one or more of the elements selected from the groupconsisting of magnesium, copper and cadmium, and

wherein the number of each element present is represented by a-d,

wherein

a is a number from 8-16;

b is a number from 0.5 to 5;

c is a number from 0.01 to 5;

d is a number from 0.01 to 5; and

e is a number that satisfies the valence requirements of the otherelements present.

Preferred catalysts are those wherein a is 12; b is between 0.5 and 3; cis between 0.01 and 1; and d is from 0.01 and 1. The elements arepresent in these catalytic compositions in the form of their oxides oroxide complexes.

In addition to the active catalytic ingredient, the catalyst of theinvention may contain a support material. Suitable support materialsinclude silica, alumina, zirconia, silicon carbide and the like. Apreferred support material is Alundum.

The catalysts of this invention are highly effective for oxidationreactions. Preferred among these reactions is the production ofunsaturated acids from the corresponding unsaturated aldehydes, and morespecifically the catalysts of the invention are capable of veryselectively oxidizing acrolein to acrylic acid.

The oxidation of unsaturated aldehydes to obtain the corresponding acidis well known in the art. Basically the invention, with respect to theprocess, is the use of the new catalyst within the parameters of theknown art process.

The known process involves the contacting of the unsaturated aldehydewith molecular oxygen in the presence of steam at a temperature of about200° to about 500° C. The ratio of the reactants may vary widely, withmolar ratios of molecular oxygen to aldehyde of about 0.5 to about 5normally being employed. Molecular oxygen is most conveniently added asair. The amount of steam may vary widely from the small amount generatedin the reaction to 20 or more moles of steam per mole of aldehyde.

The reaction may be conducted in a fixed-bed or fluid-bed reactor orforms thereof, using atmospheric, superatmospheric or subatmosphericpressure. The apparent contact time may vary considerably, with contacttimes of a fraction of a second to 20 seconds or more normally beingemployed.

As noted above, catalysts very similar to the catalyst of the inventionare known. See for example U.S. Pat. No. 4,042,533, and thus catalystsof this general type can readily be prepared by persons of ordinaryskill in the art.

Normally, the catalysts of the invention are prepared by mixing thecatalyst ingredients in the proper proportions in an aqueous mixture,drying the resulting aqueous slurry and calcining the product. Theingredients going into the preparation of the catalyst can be theoxides, halides, nitrates, acetates or other salts of the particularcompound added. If the support is used, the material comprising thesupport can be incorporated into the catalyst along with the otheringredients, or the catalyst can be coated upon a suitable supportmaterial. After the catalyst ingredients have been combined to form anaqueous slurry, the slurry is evaporated to dryness, and the dried solidobtained is heated in the presence of air at temperatures between about200° and 600° C. This calcination can take place outside of thecatalytic reactor or an in situ activation can be utilized.

SPECIFIC EMBODIMENTS Catalyst Preparation

The catalysts of Comparative Examples A through C and Examples 1-5 wereprepared according to the following procedure.

EXAMPLE 1 Catalyst Mo₁₂ V₃ Re.sub..5 Mg.sub..2 O₄₅.4

To 200 cc of hot distilled water were added 4.94 grams of ammoniummetavanadate, 29.85 grams ammonium heptamolybdate, 1.89 grams NH₄ ReO₄and 0.604 grams Mg (C₃ H₃ O₂)₂ .4H₂ O. After all the chemicals were insolution, 0.75 grams hydrazine hydrate were added. The solution was thenevaporated to near dryness with continual stirring and heating on a hotplate. The contents were then dried at 110°-120° C. overnight.

The dried material was crushed and ground to pass through a 50 meshscreen. 15 grams of this material was then coated on 3/16" Alundumspheres to achieve a 20 wt.% coating on the spheres. The coated sphereswere then dried at 110° C. for 16 hrs, and then activated by heattreating at 370° C. for 2 hrs.

The catalysts of all the examples were placed in a 20 ml fixed-bedreactor. The reactor was heated in a split block furnace. The reactorfeed was a mixture of acrolein/air/N₂ /steam in the molar ratio of1/8.5/2.5/6. The reaction was conducted at atmospheric pressure, and theapparent contact time was 2.5 seconds. The reaction temperaturesemployed and the conversions obtained are summarized in the table asfollows: ##EQU1##

COMPARATIVE EXAMPLES A-C

Comparative Example A shows that a molybdenum vanadium catalyst withoutany promoters achieves less than 50% total conversion with only 34%single pass yield to acrylic acid. When rhenium is added to the abovecatalyst as shown in Comparative Example B, both the total conversionand the single pass yield decreases. Finally, Comparative Example Cshows that when magnesium is added to a molybdenum-vanadium catalyst,there is a minor increase in total conversion and single pass yield, butthe results are still extremely low.

EXAMPLES 1-2 Rhenium and Magnesium Containing Catalysts

As shown in the Table, when both rhenium and magnesium are used topromote a molybdenum-vanadium catalyst, a totally unexpected result isobtained. The total conversion of acrolein is over 97%, with single passyields to acrylic acid as high as 92%.

EXAMPLES 3-4 Copper and Cadmium Promoted Catalysts

As shown in the Table, both copper and cadmium achieve high conversionsof acrolein with very acceptable single pass yields to acrylic acid whencombined with rhenium.

EXAMPLE 5 Double Promoted Catalysts

Example 5 shows the effect of promoting a rhenium-vanadium-molybdenumcatalyst with both magnesium and copper. Utilizing this combination,single pass yields to acrylic acid as high as 92% were obtained.

                                      TABLE                                       __________________________________________________________________________    Oxidation of Acrolein to Acrylic Acid                                                                % Copy                                                                             Single Pass Yield                                 Example                                                                            Catalyst Comp.                                                                             Temp. °C.                                                                   Acrolein                                                                           Acrylic Acid                                                                         Acetic Acid                                __________________________________________________________________________    Comp. A                                                                            Mo.sub.12 V.sub.3 O.sub.43.5                                                               356  47.6 34.2   0.9                                        Comp. B                                                                            Mo.sub.12 V.sub.3 Re.sub..5 O.sub.45.2                                                     346  36.8 28.6   0.7                                        Comp. C                                                                            Mo.sub.12 V.sub.3 Mg.sub..2 O.sub.43.7                                                     359  57.6 47.4   0.8                                        1    Mo.sub.12 V.sub.3 Re.sub..5 Mg.sub..2 O.sub.45.4                                           309  99.0 92.3   1.3                                        2    Mo.sub.12 V.sub.3 Re.sub..75 Mg.sub..3 O.sub.46.4                                          333  97.6 86.2   2.4                                        3    Mo.sub.12 V.sub.3 Re.sub..5 Cu.sub..5 O.sub.45.8                                           343  94.2 80.6   2.1                                        4    Mo.sub.12 V.sub.3 Re.sub..5 Cd.sub..2 O.sub.45.4                                           372  91.2 71.2   4.2                                        5    Mo.sub.12 V.sub.3 Re.sub..5 Mg.sub..2 Cu.sub..1 O.sub.45.4                                 310  98.9 92.6   1.6                                        __________________________________________________________________________

We claim:
 1. The process for the production of olefinically unsaturatedaliphatic acids by vapor phase catalytic oxidation of correspondingolefinically unsaturated aliphatic aldehydes with molecular oxygen, saidreaction occurring over an oxidation catalyst represented by thefollowing formula:

    Mo.sub.a V.sub.b Re.sub.c X.sub.d O.sub.e

whereinX is one or more of the elements selected from the groupconsisting of magnesium, copper and cadmium, and whereinthe number ofeach element present is represented by a-d; whereina is a number from8-16; b is a number from 0.5 to 5; c is a number from 0.01 to 5; d is anumber from 0.01 to 5; and e is a number that satisfies the valencerequirements of the other elements present.
 2. The process of claim 1wherein a is 12; b is a number from 0.5 to 3; c is a number from 0.01 to1; d is a number from 0.01 to 1; and e is a number that satisfies thevalence requirements of the other elements present.
 3. The process ofclaim 1 wherein the unsaturated aliphatic acid is acrylic acid and theunsaturated aldehyde is acrolein.
 4. The process of claim 1 wherein X ismagnesium.
 5. The process of claim 1 wherein X is magnesium and copper.